A suicide car bomb hit two diplomatic vehicles entering the Indian Embassy in Kabul on Monday, killing or wounding at least 30 people, witnesses and Afghan media said.

Taliban insurgents have vowed to step up their campaign of suicide bombings this year to overthrow the pro-Western Afghan government and drive out foreign forces.

The bomber struck just as two diplomatic vehicles were entering the embassy, said Danish Karokhil, the head of the independent Pajhwok news agency, whose offices are close by.

"The target was the diplomatic vehicles. They were trying to get inside the embassy when the suicide car bomber attacked them," he said.

"There are many people killed and wounded, the police guards protecting the embassy were also hurt. I saw wounded and dead people everywhere on the road."

Some 30 people were either killed or wounded, the private Tolo TV station said.

The two embassy vehicles were destroyed by the blast, but it was not clear if those inside were among the casualties.

A line of people waiting for visas and those shopping at a nearby market were among those hurt.

Smoke came from the scene of the blast. Police cordoned off the area as ambulance crews carried away several wounded. U.S. troops were also at the scene.

India has close relations with the Afghan government and is funding a number of large infrastructure projects.

Afghan officials have repeatedly accused Pakistan of allowing the Islamist Taliban militia to operate from sanctuaries on the Pakistani side of the border, a charge Pakistan denies.